In different technical fields, products are employed or utilized that have a specific service life as a function of the loading to which they are subjected to during their operation. A product encompasses a plurality of components. A product may be a personal computer (PC), the components then being the electrical components (power supply, main board, hard disk, disk drive, CD-ROM drive, DVD drive, etc.) of the PC. It would also be POSSIBLE, for example, to regard the main board as the product, the different electrical components, soldering points, etc. on the board then being the components. A product could also be any motor-vehicle component, in particular a motor-vehicle control unit, the components then being the different electrical components (e.g., resistors, capacitors, inductance coils, operational amplifiers), soldering points, circuit traces, etc.
The service life of a product is a strong function of the loading, to which the product is subjected during its life. For instance, a motor-vehicle control unit, which is situated in the vicinity of an internal combustion engine of a vehicle, is subjected to a substantially higher thermal loading than a control unit situated in the passenger compartment of the vehicle. The thermal loading may be an absolute temperature, but also a temperature fluctuation. The same control unit would therefore have a shorter service life in the region of the engine than in the passenger compartment. The same also applies to mechanical and chemical loadings, as well as to any other form of loading.
It is conventional that a reliability verification can be produced for a product by subjecting it to a specific, predefinable, absolute or cyclical loading for a particular, specifiable period of time, or at predefinable intervals. Therefore, to provide a reliability verification, it is determined whether a product or the components of the product is/are able to withstand a predefinable loading for a specifiable period of time.
Such reliability verifications are provided according to manufacturer-specific or customer-specific standards, or according to legally prescribed standards. To provide the verification for a product, the product should ideally be subjected to the loading to which it will be subjected within the scope of its intended use or application over a required minimum service life. If the product survives under such loading for the minimum service life, then the reliability verification for this product has been established. If it fails prior to reaching the minimum service life, the verification is not able to be produced. The testing to supply the verification may be implemented on a multitude of products having the same design, so that the result of the verification is more representative.
However, due to time restraints, it is usually impossible to run through the entire required minimum service life of the product (e.g., 15 to 20 years in the case of a motor-vehicle control unit) in real time, under the loadings occurring within the scope of its normal use or application. For this reason, it is conventional that the loadings can be increased beyond the loadings likely to occur, and that the testing period can be reduced in exchange. This is also referred to as an accelerated reliability verification.
However, the precise relationship between increased loading and shortened testing period is not known and may behave completely differently for different loadings and for different products. Furthermore, this procedure results in an accumulation of errors that are a result of the increased loadings and, in reality, do not occur during normal operation or use of the product. Such errors are also called errors irrelevant to field conditions. On the other hand, due to the shortened testing duration, certain errors that occur in reality as a result of long-term, but lower-magnitude loadings, may not occur during the shortened testing period. In other words, the shorter the testing time, the further removed the result of the verification is from reality or field conditions. That is to say, there is a conflict of goals between the shortening of the testing duration on the one hand and the effectiveness of the test results' simulation of field conditions on the other hand.
After the testing of a multitude of identical components, the conventional method provides statements, such as: “At absolute operating temperatures of above 90° C., there is a 97% probability of the product achieving a minimum service life of 5,000 hours of operation.” However, the conventional method cannot provide any statements beyond that. Such statements relate, for instance, to questions as to how long the life expectancy of the product is at a predefined loading; how long the product functions at a lower or higher loading; and which components have to be dimensioned in a certain manner for the product to achieve a higher minimum service life (which components must be built more robustly?) or to be able to be manufactured in a more cost-effective manner (which components can be built less robustly?).